It seems to me that, for Famitsu, simplicity goes a long way. For them, it was simple, nothing complex. It was a new region to explore (not a revisit to Kanto through a southern exit of an area that previously wasn't there). There was no growing Berries, no Pokéblocks, a limited number of Berries to get in-game and once a day in some cases, and so on. The map, once you reach Nimbasa City, is circular; you don't do a lot of backtracking (except once to Desert Resort and then to Nacrene, though by now you have Fly), and it's a generic path you follow without having to go back to other areas. In other words, simple. And that might be their rating system: simplicity.
I personally think a game like Crystal, if it were made in today's mapmaking format instead of the way it was at its time, would be a 40/40 game easily. However, keep in mind that after beating the Elite 4, you have to tackle another eight Gyms, another batch of new challenges, another 30 routes or whatever, more complex backtracking perhaps (I didn't play the ROM past the path to Victory Road for some reason, likely due to changing systems), and so on - things that complex what to that point has been a more simple game. Therefore, it would get a 35 from Famitsu instead of the 40 it deserves (what DID it get, NEway?). I think Black/White, given they introduce a new generation and some new combination types (Rock/Fighting for instance), might be able to get a 35; the sequels probably won't because you end up revisiting areas, and some people will say you shouldn't get Black or White now, you're already visiting the same areas you did then, or don't bother with the new ones if you have the originals because it's mostly the same game, blah blah. Of course, we know better. What I've seen of the sequels uses the old areas in hew ways (meteors in one route and Route 4 construction completed, for example). It makes for a similar experience, like revisiting Kanto from Johto, but still encompasses the same area making it a new experience in some ways. Also, the entire path to the Pokémon League is changed; what exactly is in the north part of Opelucid City now? Route 2 is changed to force you through the wild grass by making the old cliff jumps unwalkable. Things like that. It's a fresh experience in a familiar area. And Black 2 / White 2 should get a 45 if B/W gets a 40.
Cyclone